1. Field of the Invention
The present invention relates to a high frequency surface acoustic wave device and the substrate thereof and, more particularly, to a high frequency surface acoustic wave device, which does not require the conventional and expensive sapphire substrate as its substrate.
2. Description of Related Art
Please refer to FIG. 1A and FIG. 1B, wherein FIG. 1A is a perspective view of the conventional high frequency surface acoustic wave device and FIG. 1B is a cross-section view taken along the A-A′ plane of FIG. 1A. As shown in FIG. 1A and FIG. 1B, the conventional high frequency surface acoustic wave device 1 comprises: a substrate 11; a piezoelectric layer 12 forming on the surface of the substrate 11; an input transformation unit 13; and an output transformation unit 14. The input transformation unit 13 and the output transformation unit 14 are formed in pairs on the surface of the piezoelectric layer 12. The input transformation unit 13 and the output transformation unit 14 are both interdigital electrodes, and thus an interdigital transducer is formed. Besides, in the conventional high frequency surface acoustic wave device 1, substrate 11 of the high frequency surface acoustic wave device 1 is a sapphire substrate. The piezoelectric layer 12 is a ZnO, AlN, LiNbO3 or LiTaO3 film, having the thickness preferably between 0.1 μm and 10 μm. Moreover, the input transformation unit 13 and the output transformation unit 14, which are formed in pairs on the surface of the piezoelectric layer 12, are made of aluminum, with their line width being between 0.1 μm and 5 μm.
However, since other opto-electronic applications, such as a light emitting diode, also require the sapphire substrate as the substrate thereof, the price of the sapphire substrate increases a lot, and the supply of the sapphire substrate to the market is not stable, either. As a result, by using the sapphire substrate as its substrate, the manufacturing cost of the conventional high frequency surface acoustic wave device cannot be lowered, and the manufacturing process may also be forced to halt, due to the sapphire substrate often becoming out of stock.
Therefore, a high frequency surface acoustic wave device that can remove the requirement of the expensive sapphire substrate as its substrate is required, for lowering the manufacturing cost of a high frequency surface acoustic wave device.